Plasma processing of semiconductor wafers in the manufacture of microelectronic integrated circuits is used in dielectric etching, metal etching, chemical vapor deposition and other processes. In semiconductor substrate processing, the trend towards increasingly smaller feature sizes and line-widths has placed a premium on the ability to mask, etch, and deposit material on a semiconductor substrate, with greater precision.
Typically, etching is accomplished by applying radio frequency (RF) power to a working gas supplied to a low pressure processing region over a substrate supported by a support member. The resulting electric field creates a reaction zone in the processing region that excites the working gas into a plasma. The support member is biased to attract ions within the plasma towards the substrate supported thereon. Ions migrate towards a boundary layer of the plasma adjacent to the substrate and accelerate upon leaving the boundary layer. The accelerated ions produce the energy required to remove, or etch, the material from the surface of the substrate. As the accelerated ions can etch other components within the processing chamber, it is important that the plasma be confined to the processing region above the substrate.
Unconfined plasmas cause etch-byproduct (typically polymer) deposition on the chamber walls and could also etch the chamber walls. Etch-byproduct deposition on the chamber walls could cause the process to drift. The etched materials from the chamber walls could contaminate the substrate by re-deposition and/or could create particles for the chamber. In addition, unconfined plasmas could also cause etch-byproduct deposition in the downstream areas. The accumulated etch-byproduct can flake off and result in particles. To reduce the particle issues caused by the deposition of etch-byproduct in the downstream areas, additional downstream clean is needed, which could reduce process throughput and increase processing cost.
Confined plasmas could reduce chamber contamination, chamber cleaning and improve process repeatability (or reduce process drift). Plasma confinement devices, such as slotted plasma confinement ring (described below), have been developed to confine plasma. Certain front end of line (FEOL) applications, such as contact etch and high aspect ratio trench etch, require relatively low process pressure (e.g. ≦30 mTorr) under relatively high total gas flow rate (e.g. between about 900 sccm to about 1500 sccm). Plasma confinement devices, such as a slotted plasma confinement ring, could cause flow resistance for the gas flow to the downstream and results in pressure in the plasma chamber that is not low enough (e.g. ≦30 mTorr) for the FEOL applications described.
Therefore, there is a need for an improved method and apparatus that not only confine plasma within a processing region inside the plasma chamber but also enhance flow conductance.